Field of the Invention
The present invention generally relates to a method of manufacturing a light rotor shaft for eco-friendly vehicles and, more particularly, to a method of manufacturing a light rotor shaft for eco-friendly vehicles, which is formed to have stepped inner and outer diameters to reduce rear remnants.
Description of the Related Art
Recently, as environmental problems have emerged as a global issue, research into vehicle technologies that reduce exhaust emissions and improve fuel efficiency have been actively conducted. Generally, eco-friendly vehicles such as hybrid vehicles, electric vehicles, fuel-cell vehicles, or the like have been studied. Typically, eco-friendly vehicles are driven by a motor that is electrically powered from a battery to produce rotary drive power. The rotary drive power is in turn transmitted to the axles via a reducer (e.g., transmission). To improve fuel efficiency and development of eco-friendly products, the operation efficiency of high-capacity motors of eco-friendly vehicles should be improved. Improvement in the fuel efficiency of such vehicles may be achieved by producing a light rotor shaft for the motor.
FIGS. 1A and 1B are exemplary cross-sectional views showing a conventional hollow rotor shaft according to the related art. As shown in FIGS. 1A and 1B, the rotor shaft is formed into a hollow-type body to reduce the weight-of the shaft. However, the rotor shaft has a constant inner diameter, so a middle portion thereof is required to be thick, which contributes to an increased weight. Conventional methods to reduce the weight include radial forging to form a hollow body having stepped inner and out diameters.
FIG. 2 illustrates an exemplary schematic illustrating the conventional radial forging method according to the related art. FIGS. 3A and 3B illustrate exemplary cross-sectional views, including a defective folded section of a hollow body manufactured using the radial forging method according to the related art. As shown in FIGS. 2 and 3A and 3B, the radial forging method includes forming a preform, inserting a mandrel into the preform first press-forging an outer diameter part of the perform, into which the mandrel has been inserted, to draw the outer diameter part in one direction. The mandrel is removed and the outer diameter part is then second press-forging, thereby forming a hollow product. However, in the second press-forging the outer diameter part while removing the mandrel as shown in FIG. 3B, a problem arises. In particular, an inner diameter part is compressed and shrinks, causing the opposing surfaces of a rear circumference to adhere to each other, thereby forming a rear remnant (A), which adversely affects weight-reduction of a product. Further, such a rear remnant attributed to surfaces sticking has an elevated stress-concentration, potentially contributing to a premature failure.
The above information disclosed in this section is intended merely to aid in the understanding of the background of the invention, and therefore may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.